fredag 31 augusti 2012

My book The Secret of Flight, coauthored with Johan Hoffman and Johan Jansson, is going to appear on Dover Publications late this year or beginning next year in print edition. A draft of the book is available here. Comments are welcome.

The book is based on the article New Theory of Flight submitted to AIAA Journal presently in the second round of the referee process.

Here is the impression by editor Rochelle Kronzek at Dover:

I was at the library two days ago doing some research when I came upon your just posted book, "The Theory of Flight". What an absolutely delightful book, Claes!! We at Dover are very interested in publishing this work for you and your co-authors when you feel ready to do so.

I want to report that your book " Numerical Solution of Partial Differential Equations by the Finite Element Method " is doing very well indeed. I am so very proud to have it as a part of our list for nearly three years now. Amazon is the number one conduit for your book's sales!

torsdag 30 augusti 2012

The Royal Institute of Technology (KTH), where I am prof em of applied mathematics, has made it clear that a link to the ebook Mathematical Simulation Technology (MST), on the course page of a third year course on the finite element method given by one of the authors of the ebook, the link being intended as a service to interested students, is not allowed. Any such link will be deleted, by KTH.

The event in the Fall 2010 described as KTH-gate, when the same link was deleted, is now repeating itself in a new round described as KTH-gate2. In 2010 the censorship was motivated by the presence of some examples of mathematical climate modeling in MST doomed by KTH as unacceptable, however without any form of specification. Now in 2012 no motivation is given.

Internet censorship is the control or suppression of the publishing of, or access to information on the Internet. It may be carried out by governments or by private organizations at the behest of government, regulators, or on their own initiative.

The reason for the suppression of MST by KTH is that MST presents an alternative to the traditional teaching of mathematics and physics, where modern computational techniques are combined with traditional analytical techniques. The alternative is viewed as a threat to the traditional mathematics education by mathematicians in charge of mathematics education, and the reaction is to censor the alternative by deleting any link to MST.

That the censorship is against the very essence of an education based on principles of science, is clear. What is not is not so clear is the legal aspect of the censorship. Is it possible for a university to delete a link to an ebook written by a professor at the university against the will of the professor? With motivation? Without motivation?

PS2 It is ironic the the required text in the finite element course in question, is another book by myself: CDE. One book is applauded, another is censored, while they represent different steps in the evolution of the same material. As you can see, FEniCS as another of my initiatives, is allowed, but not MST. As is mostly the case, censorship is dumb and blind.

PS3 One way of understanding why CDE is applauded as course literature and MST is censored, while they represent essentially the same ideas only expressed at different times (CDE 1996 and MST 2010), is the following: Mathematics education is put into a squeeze between an outside demand of modernization and an inside tradition of preservation, which results in an unstable oscillation between acceptance (CDE) and rejection (MST), an instability which can only result in break-down.

Our computed solutions of Navier-Stokes/slip don't match observations. Wrong: Both lift and drag are within measurement tolerance for the whole range of angles of attack including and beyond stall.

Separation with slip is not described. Wrong: We give a clear mathematical analysis of separation in slightly viscous flow supported by computation and observation based on a fundamental instability of potential flow.

We contribute to confuse students and mislead the public. Wrong: Our theory is the first theory which can be effectively presented in education and to the general public.

There is nothing wrong with Kelvin's theorem. Yes, there is when wellposedness is taken into account, and this is necessary in a theory about physics.

The code is not documented and private: Wrong: The code (Unicorn) is part of the open source project FEniCS with solid documentation. Any interested can replicate our computations.

The authors have not studied the literature enough. Wrong: We have scrutinized most of the books and scientific articles on the subject carefully.

The authors have not discussed with their aerodynamics colleagues at KTH. Wrong: Extensive discussion have taken place over a long period of time.

put their fingers accurately on many of the defects in the truncated versions of aerodynamic theory that are now current...explanations stimulated by interesting results from their Navier-Stokes code...computational experiments, which are three-dimensional as, of course, are real wings...computer code that is their basis for disputing the classical theory. This is their area of expertise, and it may be assumed that their description is accurate...the authors are correct that separation might be fundamentally different in 3D than in 2D...serious issues of substantial public interest are involved.

lost profundity...no longer highly respected...many gaps...truncated version...glossed over...defects...proliferating literature...confuse students mislead the public...dumbing down...I wish it were possible to retract what has already been written.

Editor Blaisdell is now reading our rebuttal including this post. It will be interesting to see what a careful reading will bring out. Will the rejection resist our rebuttal? Stay tuned...

onsdag 22 augusti 2012

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.

No, it is not easy to convince professors defending the Old Theory that the New Theory is better by making them see the light.

But eventually the Old Theory will be replaced by the New Theory and it is of interest to speculate about they time span required for this change. The more healthy the Old Theory is, the longer will it live, and the other way around.

So what is then the health status of the Old Theory today? What does education tell?

Well, the educational system is constructed so as to preserve the Old Theory as long as possible. As long as the Old Scientists who shaped the Old Theory are in business in their chairs at leading universities, there is nothing you can do except finding a place at some progressive college and be silent.

In aerodynamics education this phase is however passed: The Fathers of Modern Aerodynamics (Kutta-Zhukovsky and Prandtl) are all dead since 60 years, but the Old Theory is still taught at the university.

However, the Old Theory is presented in diluted eroded form as evidenced by Reviewer 2 of our article. This is because the Fathers took secrets and convictions of the Old Theory along into the grave. The result is that there is today no living scientist who can convincingly present all the details of the Old Theory. Only weak distorted memories are now retold in modern text books, according to Reviewer 2.

So the end of the Old Theory may be near: The Fathers are safely put to rest, and the Old Theory is weakened.

The same situation is met in classical Calculus education, which is today diluted into emptiness.

Also recall the following Planck quote:

New scientific ideas never spring from a communal body, however organized, but rather from the head of an individually inspired researcher who struggles with his problems in lonely thought and unites all his thought on one single point which is his whole world for the moment.

Aerodynamics today is ... almost always taught in a truncated version that ... has lost much of the profundity.

Even the truncated version is no longer as highly respected as it used to be.

In consequence, there are many employed today in the aerospace industry, and even in academia, whose grasp of the basic theory of flight contains many gaps.

These gaps are apparent to thoughtful students, who frequently attempt to fill them in for themselves, although the remedy is usually worse than the disease.

I believe that the authors of the paper under review ... are right to quarrel with the truncated version that they, like others, have apparently received.

The relationship between potential flow and real flow ... is glossed over in the great majority of contemporary texts.

The authors greatly underestimate the classical theory, most likely because the usual truncated exposition has not shown it to them in its proper light. The authors have put their fingers accurately on many of the defects in the truncated versions of aerodynamic theory that are now current.

These difficult issues were struggled with years ago by the founding fathers of the subject... Sadly, the outcomes of those struggles have since been simplified or discarded in modern presentations to create a pragmatic treatment focusing on utility.

Undergraduate textbooks these days all too often simply omit anything that students find difficult.....proliferating literature of “theories of flight” that serves only to confuse students and mislead the public.

I wish it were possible to retract what has already been written.

A book intended for specialists, but that is old enough not to have succumbed to the almost universal dumbing down, is Theory of Flight, by R. von Mises.

Reviewer 2 thus clearly expresses that the state-of-the-art aerodynamics education of today represented by AIAA and my aerodynamics colleagues at KTH, is degenerated and concludes with:

I believe that serious issues of substantial public interest are involved.

Yes, serious issues of great public interest are involved. How is now AIAA going to handle the criticism and how is AIAA Journal going to handle our article? By suppressing it? Or publishing it because of its substantial public interest?

The basic physical principles tend to be buried and replaced by mystical jargon.

Classical explanations for the generation of lift do not make the essence of the subject clear, relying heavily on cryptical terminology and theorems from mathematics.

Many classical texts even appear to have a fundamental error in their underlying assumptions.

Although the subject of lift is old, it is felt that a satisfactory general but easily understandable explanation for the phenomenon (of lift), is still lacking, and consequently there is a genuine need for one.

It is amazing that today, almost 100 years after the first flight of the Wright Flyer, groups of engineers, scientists, pilots, and others can gather together and have a spirited debate on how an airplane wing generates lift. Various explanations are put forth, and the debate centers on which explanation is the most fundamental.

Aerodynamics today is therefore almost always taught in a truncated version ... (which) has lost much of the profundity.

Even the truncated version is no longer as highly respected as it used to be.

In consequence, there are many employed today in the aerospace industry, and even in academia, whose grasp of the basic theory of flight contains many gaps.

These gaps are apparent to thoughtful students, who frequently attempt to fill them in for themselves, although the remedy is usually worse than the disease.

I believe that the authors ... are right to quarrel with the truncated version that they, like others, have apparently received.

OK, so we read that the reviewer is critical to the way state-of-the-art aerodynamics is presented today by living academic scientists with the result that the basic theory of flight is not understood by aerospace engineers. This is scary and heavy criticism of in particular AIAA by the reviewer, fully in line with the criticism of our article. So far so good from our perspective.

But then the reviewer changes gear:

All of the criticisms that comprise Section I of their paper can be answered, and I will try to do this below.

... all these difficult issues were struggled with years ago by the founding fathers of the subject, and resolved in completely satisfactory ways.

Sadly, the outcomes of those struggles have since been simplified or discarded in modern presentations to create a pragmatic treatment focusing on utility.

Undergraduate textbooks these days all too often simply omit anything that students find difficult.

The reviewer then presents a 6 page attempt of resurrection of the forgotten theory by the founding now dead fathers.

Doing so the reviewer reveals a misunderstanding of the nature and role of scientific discussion and publication. If the reviewer believes that state-of-the-art aerodynamics education is deficient and needs to be corrected, and that the reviewer has the remedy, the reviewer should make this public to the scientific community e.g. in an article submitted to AIAA Journal, instead of hiding this in anonymous form in a referee report closed to inspection.

After having so resurrected aerodynamics from its present collapse, the reviewer feels armed to kill our article by:

Regrettably, it is my conclusion that publication of any of this material, in any form, would be highly retrogressive.

What is so regrettable is however not so clear. Maybe, the reviewer is regretting to have written the review.

PS Remember that a dead scientist does not speak. Neither a dead witness in a gangster trial.

The text book theory of lift of a wing is since 100 years the Kutta-Zhukovsky Circulation Theory based on 2d potential flow modified by large scale circulation around the wing section determined by the Kutta condition of zero flow velocity at the trailing edge.

Kutta-Zhukovsky Circulation Theory is presented as a "mathematical theory" based on the "trick" of the Kutta condition, to be compared with "physical theories" commonly connected to Newton and Bernoulli. This is presented as follows:

There are several ways to explain how an airfoil generates lift. Some are more complicated or more mathematically rigorous than others; some have been shown to be incorrect....but each appeals to a different audience.(Wikipedia)

The mathematical description of lift is a general term for the analysis tools of classical aerodynamics and computation aerodynamics. If the objective is to accurately compute the principle or aerodynamics of a wing, these are the tools to use, though the aerodynamic description is mathematical and not physical. (Understanding Flight)

There are different explanations of flight: 1. Mathematical, taught to aeronautical engineers. 2. Popular, taught at flight schools, NASA, in many cases fine but wrong. 3. Physical, presented by myself in this lecture. (Jefferson Lab Science Series/Eberhardt)

Circulation theory is thus described as a mathematical theory useful for computing lift, which however is not a physical theory. This fact is typically expressed as follows:

How can potential flow be adapted to provide a reasonable theoretical model for the flow around an aerofoil that generates lift? The answer lies in drawing an analogy between the flow around an aerofoil and that around a spinning cylinder. For the latter it can be shown that when a point vortex is superimposed, a lifting flow is generated. (Aerodynamics for Engineering Students, 5th edition, by Houghton and Carpenter)

The airflow about an airfoil may be viewed as consisting of two superimposed patterns—one is the free-stream motion of the air about the airfoil and the other is a circulatory flow, or circulation, around the airfoil. (US Centennial Flight Commission)

The non-physical aspect of Circulation Theory is visible in expressions such as potential flow "be adapted" and airflow may "be viewed".

It is thus generally acknowledged that Circulation Theory does not describe the actual physics of generation of lift. When now there is a New Theory of Flight describing the actual physics in mathematical terms, which can be used to compute both lift and drag, there is no longer any need for any unphysical Circulation Theory. This will come as a relief to many who have struggled to understand Circulation Theory over the years without success.

2. Our Criticism of Prandtl's Boundary Layer Theory of Drag

Prandtl's boundary layer theory attributes drag to the presence of boundary layers. We compute drag in slightly viscous flow accordance with observation by solving the Navier-Stokes equations with slip boundary condition without presence of boundary layers. We conclude that the major part of drag (form drag) in slightly viscous flow does not originate from any boundary layer, and thus that Prandtl's theory does not cover the major part of drag in slightly viscous flow.

3. Our New Theory of Flight

The reviewers do not question that our New Theory of Flight describes real 3d flow.

What they question is our criticism of classical 2d theory: Instead of frankly admitting that it is unphysical and thus incorrect, as we do, the reviewers want to describe classical theory as correct in principle as a 2d theory, even if this 2d theory does not really describe real 3d flow. This is a common way of handling the unphysical aspect of classical 2d theory; admitting that it is 2d and thus in a sense unphysical as any model (no model is perfect) but insisting that anyway it is correct in some sense as a 2d flow model, which somehow "represents real 3d flow" without describing the actual 3d physics. Thus correct even if incorrect, as any model (no model is perfect). This is the split between theory and practice which has troubled fluid mechanics starting with d'Alembert's paradox in 1752.

The reviewers claim that a slip boundary condition does not describe the physics of slightly viscous flow. This is not correct because the skin friction of slightly viscous flow is small and slip models small skin friction. Slip is also a mathematical meaningful (and possible) boundary condition. The reviewers are stuck to a Prandtl dictate to use no-slip with lacks both mathematics and physics rationale.

Altogether, the criticism of the New Theory is weak, and the defense of the Old Theory is also weak.

Reviewer 2 offers the following starting point for the continued discussion with AIAA:

I believe that serious issues of substantial public interest are involved.

The authors have put their fingers accurately on many of the defects in the truncated versions of aerodynamic theory that are now current.

Classical theory ... is a masterpiece of physical modeling.

The authors experience great difficulty with the relationship between potential flow and real flow. This is not surprising because it is glossed over in the great majority of contemporary texts.

The present authors may be innocent of mathphobia.

I believe that the authors of the paper under review would have no quarrel with the orthodox theory if they knew all of the details, although they are right to quarrel with the truncated version that they, like others, have apparently received.

The authors have then sought their own explanations, stimulated by interesting results from their Navier-Stokes code. However, they have failed to ask questions that would have been suggested by any experienced practical aerodynamicist.

However, the authors are correct that separation might be fundamentally different in 3D than in 2D.

Section IV states that sharp trailing edges are not necessary. This will not come as a surprise to any practicing aerodynamicist.

Section V invokes scale invariance to explain how, within their theory, the lift and drag would be independent of trailing edge radius.

Section VII describes the authors computational experiments, which are three-dimensional as, of course, are real wings.

Section II describes the computer code that is their basis for disputing the classical theory. This is their area of expertise, and it may be assumed that their description is accurate.

This review is very much longer than I would normally write, because I believe that serious issues of substantial public interest are involved.

This gives substantial credit to the article but does not fit with the conclusion of the reviewer that

that publication of any of this material, in any form, would be highly retrogressive.

What seems unacceptable to AIAA is critique of state-of-the-art voiced by a research group which is not part of state-of-the-art. Internal critique is ok but not external. This is characteristic of a closed hierarchical society. This is expressed by the reviewer:

They should make the test of running their code in 2D mode, which would eliminate their explanation but leave other explanations in place.

So, classical theory is 2d, but real wings are 3d as is our theory. Restriction to 2d would leave classical explanations in place but would not concern real wings. I think this is a good summary of the reviewers position, offered by the reviewer. It means that classical theory is unphysical but correct as an unphysical theory.

But if anything the New Theory of Flight does not go back to an earlier condition, which is signified by the fact that it is New.

Further, the statement that publication of any of this material in any form would be highly retrogressive, would in order to be motivated seem to require that every single line of the article is old stuff. But this is not so.

The response from the New York Times is merely irresponsible journalism, but undoubtedly an air of mystery does pervade flight, and the attempt to dispel it by simplified accounts does as much harm as good. The present authors may be innocent of mathphobia; nevertheless they unfortunately feed the flames of irresponsible journalism. All of the criticisms that comprise Section I of their paper can be answered, and I will try to do this below.

Yes, it is true that the classical theory of flight has paralyzed modern aerodynamics by mathphobia, but it is not the criticism which is pathological.This is in fact acknowledged by the reviewers:

The authors have put their fingers accurately on many of the defects in the truncated versions of aerodynamic theory that are now current.

This alone could have motivated publication of our article, which however would be meaningless because

...all these difficult issues were struggled with years ago by the founding fathers of the subject, and resolved in completely satisfactory ways.

But if everything was resolved by the founding fathers, what role has then AIAA to serve today?

lördag 18 augusti 2012

Power play is commonly used in academic debate: Insinuations from your opponent that you are ignorant and does not have the same full grasp of theories and literature as the opponent, can be very effective, or at least can be believed to be effective.

I believe the reviewers have treated your paper fairly and have given thoughtful, well-reasoned critiques of your paper. They have not been simply dismissive in their response. I hope you will follow their suggestions for further reading so that you may better understand the basis of their remarks.

Given the criticisms the reviewers have brought up, I do not see how you could successfully rebut their comments. However, I am willing to read a rebuttal, if you think you can refute what they have said. Before doing so, I would encourage you to read the references the reviewers cite and to discuss the issues with your colleagues in the Aeronautics or Mechanics Departments at KTH, as the reviewers suggested.

If after having done that, you think the comments of the reviewers are not valid, then I would be willing to listen. However, I think you would have a difficult time convincing me that the reviewers are mistaken.

I do not want you to waste your time, since I seriously doubt any rebuttal would be successful. However, in the spirit of scientific inquiry, if you truly think the reviewers' comments

are not valid and can prove that, then I would be willing to listen.

This is power play: The editor states what is obviously not true, that the reviews are thoughtful, well-reasoned and not simply dismissive, and then paternally suggests that we should read the literature and then come back. The editor discourages any rebuttal attempt, without knowing what we have to say, but in the spirit of scientific inquiry cannot butallow it.

Concerning literature, The Secret of Flight gives an account of the literature the authors have scrutinized under Text Book Theory and New Posts.

Power play is risky, because you can use that technique yourself and ask your opponent about math books which you can claim to master and your opponent has not even heard of.

Let us as a start to a second round, after a first round of rejection based on reports by reviewers which do not show competence, analyze the present situation:

1. Accepting the article would mean that AIAA views the New Theory to be more correct than the Old Theory advocated by AIAA, and thus would require a reorientation of AIAA. This would be difficult for the inner circle of AIAA and aerodynamics to accept, since our group is an outsider.

2. Rejecting the article on loose grounds as of now, may not be clever if it turns out that after all the New Theory is better than the Old Theory.

3. Opening to a scientific discussion, as now editor Blaisdell seems to be willing to do, is dangerous for AIAA since the referee reports are filled with misconceptions and misrepresentation which can solidly be rebutted.

So will AIAA now accept or reject? Today rejection would seem to be the only possibility, independent of the strength of our article and the weakness of the referee reports. But rejection is not possible in a longer perspective because our scientific evidence is mathematical and in an open scientific discussion this is as unstoppable as a principle of democracy in an open society.

Navier-Stokes with slip is a computable mathematical model which describes slightly viscous flow and thus opens to computational exploration of aerodynamics. This is to be compared with the state-of-the-art dictate by Prandtl to use no-slip, which has made Navier-Stokes uncomputable by requiring resolution of thin boundary and thus has blocked progress for a century. This is acknowledged by one of the reviewers.

Navier-Stokes/slip predicts drag and lift of a wing over the full range of angles of attack within the tolerance of experimental observation. This is new and offers a new tool to the design of airplanes, boats and wind turbines.

The state-of-the-art lift theory by Kutta-Zhukovsky relies on a "trick" which is mathematically incorrect (demanding a no-slip condition of inviscid flow) and physically incorrect (2d flow).

The state-of-the-art theory of drag by Prandtl attributing drag to boundary layer effects is incorrect, since Navier-Stokes/slip gives correct drag without boundary layers.

The true 3d separation mechanism at the trailing edge resulting from a basic instability of potential flow.

Unification of mathematical theory and observed aerodynamics, in contrast to the split which has troubled fluid mechanics since its start with d'Alembert's paradox.

Leading frontier computational technique of duality based adaptive stabilized finite element methodology implemented in well document open source software (Unicorn/FEniCS).

True physical explanation of the generation of large lift/small drag of a wing, which can be presented to a general audience in understandable form.

Concrete possibility reform of aerodynamics education with new text books combining mathematics, computation and physics into a new synthesis.

Finally, the article is a product of a world leading group in computational fluid dynamics.

fredag 17 augusti 2012

As a first reaction to the rejection of our article New Theory of Flight submitted to AIAA J, I asked the assigned editor Greg Blasidell the following:

Dear Prof BlaisdellAre you open to a discussion about the referee's reports or is the case closed?

Sincerely,

Claes Johnson

I received the following answer:

Professor Johnson,Given the criticisms the reviewers have brought up, I do not see how you could successfully rebut their comments. However, I am willing to read a rebuttal, if you think you can refute what they have said. Before doing so, I would encourage you to read the references the reviewers cite and to discuss the issues with your colleagues in the Aeronautics or Mechanics Departments at KTH, as the reviewers suggested. If after having done that, you think the comments of the reviewers are not valid, then I would be willing to listen. However, I think you would have a difficult time convincing me that the reviewers are mistaken.

I want to make it clear that I am not encouraging you to try to rebut the reviewers' comments. I do not want you to waste your time, since I seriously doubt any rebuttal would be successful. However, in the spirit of scientific inquiry, if you truly think the reviewers' comments are not valid and can prove that, then I would be willing to listen.

Sincerely,

Greg Blaisdell
I therefore renew my questions to Professors Rizzi and Ringertz who represent the highest scientific expertize on the aerodynamics of flight at KTH. To help the process I sent the
following request to AIAA:

Thanks for your response. I have asked Prof Rizzi and Ringertz asexpertize to express their view on our work, however to no effect. It would now seem logical that you on behalf of AIAA make this request directly. Can you do that?

A professor at a Swedish university is supposed to respond to questions within his/her area of expertise, in particular to serious questions from a professor in a related area, and so the silence is very remarkable.

torsdag 16 augusti 2012

The authors provide no documented scientific evidence to discredit the current state of the art.

Yes, we do and we are not alone: Very substantial criticism of the Kutta-Zhukovsky-Prandtl theory of lift has been expressed by many scientists ever since this theory was conceived 100 years ago.

The reviewer then branches out into a sequence of incoherent statements without meaning:

First of all, the concept of circulation is not necessary for the physical explanation of lift-the physical Kutta condition leads to the correct (as verified by experiment) solution to the potential flow problem. Circulation enters the mathematical problem for the incompressible potential flow past an airfoil since the problem is non-unique without its specification.

More importantly, Prandtl’s boundary-layer theory is not a viscous theory for drag but an

asymptotic theory for the solution to the Navier-Stokes equations at large Reynolds number.

Potential flow is not presented as the solution for lift but as the first term in an asymptotic expansion - the potential flow and boundary-layer theories are connected through the matching process.

The versions of potential theory and boundary-layer theory the authors present are only the first terms in the expansion.

Their claim that the theories of Kutta-Joukowski and Prandtl are both incorrect at “separation” (undefined by the authors but apparently only considered at the trailing edge) does not take into account the extensive research into the potential flow-boundary-layer coupling.

In fact, the inclusion of the effect of the displacement thickness in the second-order potential flow solution renders arguments associated with a trailing-edge stagnation point moot. (The trailing edge stagnation point does not appear for a cusped trailing edge).

In addition, problems arising with the calculation of the boundary layer past the trailing edge or a separation point are addressed with a strong-interaction version of the boundary-layer equations (see the discussion in Chapter 14 of Katz and Plotkin which also includes a detailed discussion of the matching process referred to above).

After this excursion into terra incognita the reviewer returns to our article:

The authors’ new approach is to solve the Navier-Stokes equations numerically with an unphysical slip boundary condition.

The authors must demonstrate that the slip boundary condition somehow matches the physics of viscous flow near a solid boundary. They do not do this.

Yes, this is precisely what we do. We show that slip models the small skin friction of slightly viscous flow and that solution of Navier-Stokes with slip matches observation. This is a key point of our article.

The reviewer concludes with

In summary, the authors have not presented us with an aerodynamic theory alternative to the modern boundary-layer theory in the literature which addresses lift and drag.

At most, perhaps they present a numerical model of the governing equations which avoids the need to discretize the boundary layer.

They would however need to demonstrate how drag is calculated with such a model and that the results match with detailed experiments.

The reviewer has understood one of our major points: Discretization of the boundary layer is not necessary, which makes it possible to solve the Navier-Stokes equations with millions of mesh points, instead of the impossible quadrillions required by state-of-the-art. But the reviewer then falls back to misunderstanding: We compute both lift and drag for all angles of attack in close correspondence to observation.

Altogether, this is a very poor report by a reviewer who misrepresents key aspects of the article. The report does not meet the standards of AIAA as The World's Forum for Aerospace Leadership.

All of the criticisms that comprise Section I of their paper can be answered, and I will try to do this below.

The defense contains many remarkable and incorrect statements with my comments in parenthesis:

There is a mathematical subtlety involved because the flow of a fluid at infinite Reynolds number (zero viscosity) is not always the same as the limit at very small viscosity (it is a singular perturbation problem), and so the question is what light can be shed by the former on the latter? (This is so subtle that it is meaningless.)

There is no way to create vorticity within a viscous incompressible fluid. Vorticity can be created only at a solid boundary. (This is incorrect as shown on Kelvin's Theorem Unphysical.)

In the limit of vanishingly small viscosity, the boundary layer has no thickness, but is still present as an infinitesimal layer of infinite vorticity and hence making a finite contribution to circulation. (Meaningless statement.)

Vorticity can be created only at a solid boundary. It travels into the interior solely by diffusion....There is a tendency to suppose that the vorticity must be spread by viscosity, which does not seem plausible...(Contradiction.)

But what happens is that the circulation at infinity is set up by acoustic waves, and, if the flow really were incompressible, these travel infinitely fast. What acoustic waves cannot do is create vorticity. (Mind boggling.)

The authors greatly underestimate the classical theory, most likely because the usual truncated exposition has not shown it to them in its proper light. If they take time to realize how its parts fit together, they will come to see that is a masterpiece of physical modeling. (The reviewer greatly overestimates classical theory; if it was such a masterpiece the reviewer's rescue operation would not be needed.)

The real flow (by which they mean their computed flow) always contains a boundary layer whose influence is not negligible at any Reynolds number. This is characteristic of singular perturbation problems, and is the reason why Prandtl’s insight was transformative to the theory of flight. (This is incorrect and is precisely the key element of our criticism of Prandtl which the reviewer does not address.)

As described earlier, the desirability of the sharp edge lies in forcing the boundary layer to negotiate an adverse pressure gradient before it could reach any other stagnation point. It is not necessary for the trailing edge to be absolutely sharp to achieve this aim. But the shaper the edge is, the more certain the effect, and the more likely to remain effective at high angles of attack. (This is incorrect. If it was correct that only a sharp trailing edge would a have a "certain effect", there would be no air transportation.)

The “trick” (Kutta condition) if it deserves to be so called, lies in condensing this to a simple boundary condition, the effect of which is to force the zero-viscosity solution to obey the boundary condition for the small-viscosity solution. (This is incorrect as shown on The Kutta Trick is Illegal.)

It is well known that it is extremely hard, and probably impossible, to produce two-dimensional flow experimentally. It should be, and usually is, impossible to produce it in a three-dimensional computation. (Confusion about the non-physical 2d problem, which lacks all relevance.)

Calculations of this kind (Unicorn) are often referred to as Implicit Large Eddy Simulation, and are a recognized, but somewhat controversial, approach to modeling some aspects of turbulence. Is that what is being done? In any case, the mere fact of vorticity being observed means that the code did not simulate a potential flow. (Total confusion concerning the computational solution of the Navier-Stokes equations supporting the theory.)

There follows a stability analysis of the linearized Euler equations. This is of doubtful validity (But is it valid?) because it assumes that a perturbation with non-zero curl can be introduced into an irrotational flow. Physically this cannot be done; I have already explained that there is no mechanism even within the Navier-Stokes equations for vorticity creation, merely the evolution of vorticity already present. Creation must take place at solid surfaces and involve viscosity, or must require externabody forces. There is nothing at all wrong with Kelvin’s Theorem. (Yes, it is, seeKelvin's Theorem Unphysical.)

Regrettably, it is my conclusion that publication of any of this material, in any form, would be highly retrogressive. (Not anything in any form?)

The authors have put their fingers accurately on many of the defects in the truncated

versions of aerodynamic theory that are now current. (Compare previous statement)

However, they have not realized that all these difficult issues were struggled with years ago by the founding fathers of the subject, and resolved in completely satisfactory ways. (Incorrect, as shown by the reviewers attempt to rescue the fathers)

Sadly, the outcomes of those struggles have since been simplified or discarded in modern presentations to create a pragmatic treatment focusing on utility. (Yes, it is a sad state-of-the-art.)

This review is very much longer than I would normally write, because I believe that serious issues of substantial public interest are involved. (Yes the issues are important and require reviewers with deep insight into both mathematics, computation and fluid mechanics, and Reviewer 2 does not meet these requirements.)

Summary: The reviewer has not read and understood the article. The reviewer seeks to stop the article, because it questions the dogmas set by the fathers of aerodynamics 100 years ago. We share the criticism with many, but we are unique by offering a new correct understandable theory of flight backed by solid math, computation, physics and observation. It is not very clever by AIAA to dismiss our work on loose grounds. It will not disappear.

The reports give ample evidence that the existing theory is insufficient. Reviewer 2 starts out with

The classical theory of flight is no longer of interest to mathematicians, because they know that it has been a solved problem for many decades (although they have forgotten the details).

Obviously, it remains of interest to engineers on account of its predictive ability, but it can be employed very successfully without knowledge of the subtleties.

Aerodynamics today is therefore almost always taught in a truncated version that retains all of the utility, but has lost much of the profundity.

Even the truncated version is no longer as highly respected as it used to be, because Computational Fluid Dynamics delivers, with no requirement for deep thought, most of the practical answers that are needed.

In consequence, there are many employed today in the aerospace industry, and even in academia, whose grasp of the basic theory of flight contains many gaps.

These gaps are apparent to thoughtful students, who frequently attempt to fill them in for themselves, although the remedy is usually worse than the disease.

I believe that the authors of the paper under review would have no quarrel with the orthodox theory if they knew all of the details, although they are right to quarrel with the truncated version that they, like others, have apparently received.

What Reviewer 2 effectively says is that the theory of flight is a mess, abandoned by mathematicians and not understood by engineers designing airplanes. This is serious criticism of the existing theory, by the reviewer.

Reveiwer 2 then continues by dismissing the criticism published in AIAA J and NYT/John D. Anderson (and many other places)

The authors’ citation from Hoffren reveals the unfortunate “mathphobia” that many critics display.

The response from the New York Times is merely irresponsible journalism, but undoubtedly an air of mystery does pervade flight, and the attempt to dispel it by simplified accounts does as much harm as good.

Reviewer 2 then pleads for mysticism instead of science:

Understanding flight requires intuiting the behavior of an intangible medium for which our evolution has provided no apt language.

Finally, Reviewer 2 starts out into a lengthy attempt to resurrect the theory that has collapsed:

All of the criticisms that comprise Section I of their paper can be answered, and I will try to do this below.

Reviewer 1 dismisses our article by

The authors provide no documented scientific evidence to discredit the current state of the art.

Reviewer 1 thereby dismisses all the criticism of the current state of the art, acknowledged by Reviewer 2, and expressed by AIAA/Hoffren among many.

They do not show that they have read and understood our arguments, which is necessary to give an evaluation. Instead they display a large number of misconceptions as concerns both mathematics and computation underlying the theory of flight. I will return to these misconceptions in an upcoming post.

Our article New Theory of Flight submitted to AIAA Journal has been rejected with the following letter:

03-Aug-2012Dear Dr. Hoffman:I am sorry for not responding sooner to your email. I have been out oftown for the past several weeks.I write you in regards to manuscript # 2012-03-J051947 entitled "NewTheory of Flight" which you submitted to the AIAA Journal.In view of the criticisms of the reviewer(s) found at the bottom of thisletter, your manuscript has been declined for publication in the AIAAJournal.Please carefully read the attached reviews. Your paper is unusual in thatit challenges our existing understanding of aerodynamics. I believe thereviewers have treated your paper fairly and have given thoughtful,well-reasoned critiques of your paper. They have not been simplydismissive in their response. I hope you will follow their suggestionsfor further reading so that you may better understand the basis of theirremarks.Thank you for considering the AIAA Journal for the publication of yourresearch. I hope the outcome of this specific submission will notdiscourage you from the submission of future manuscripts.Sincerely,Greg BlaisdellProf. Gregory BlaisdellAssociate Editor, AIAA Journalblaisdel@purdue.edu
Here are the two referee reports for inspection: AIAAreview1 and AIAAreview2.

The reports offer interesting reading as evidence of the state-of-the-art represented by AIAA.

My analysis of the reports and the rejection letter will follow shortly....

Is AIAA open to a discussion or is the discussion closed with the above letter and reviews?

Note that Blaisdell acknowledges that our paper is unusual in that it challenges our existing understanding of aerodynamics. The question is if it is possible to challenge the existing understanding or if it is simply dictated by AIAA?

tisdag 14 augusti 2012

The United States Congress charges the Commission with playing the leading role in coordinating and publicizing activities celebrating the achievements of Wilbur and Orville Wright and commemorating a century of powered flight.

Use our Web site to access the most up-to-date information on celebration activity as well as the most comprehensive collection of outstanding educational essays, multimedia and links regarding the history of flight.

The airflow about an airfoil may be viewed as consisting of two superimposed patterns—one is the free-stream motion of the air about the airfoil and the other is a circulatory flow, or circulation, around the airfoil.

These two flows coexist to give the total flow pattern.

The question is, if the free-stream flow is prescribed or set, can the circulation, represented by G be of any value?

A physical condition provides the answer. The flow about the pointed trailing edge cannot turn a sharp corner without the velocity becoming infinite.

As this is not possible in real airflow conditions, the flow instead leaves the trailing edge tangentially and smoothly.

This is the Kutta condition and it sets the required value of G so that the rear stagnation point moves to the trailing edge.

The Theory of Flight has thus not changed over a century, while the Practice of Flight has evolved through several generations of revolution. This is only possible with a theory well separated from reality, as shown on The Secret of Flight.